JPWO2013157418A1 - SiC single crystal and method for producing the same - Google Patents

Abstract

An object of the present invention is to provide a high-quality SiC single crystal with reduced threading dislocation density such as screw dislocations, edge dislocations, and micropipe defects, and a method for producing such a SiC single crystal by a solution method. A method for producing a SiC single crystal by a solution method, wherein a SiC single crystal is grown by bringing a SiC seed crystal into contact with a Si-C solution having a temperature gradient that decreases in temperature from the inside toward the surface. The temperature gradient of the surface region is set to 10 ° C./cm or less, the (1-100) plane of the SiC seed crystal is brought into contact with the Si—C solution, and the SiC single crystal is formed on the (1-100) plane of the seed crystal. Is grown at a ratio of the growth rate of the SiC single crystal to the temperature gradient (single crystal growth rate / temperature gradient) of less than 20-10 <-4> cm <2> /h.degree. C. .

Description

  The present invention relates to a SiC single crystal suitable as a semiconductor element and a method for producing the same, and more particularly to a high quality SiC single crystal with few threading dislocations and a method for producing a high quality SiC single crystal by a solution method.

  SiC single crystals are very thermally and chemically stable, excellent in mechanical strength, resistant to radiation, and have excellent physical properties such as higher breakdown voltage and higher thermal conductivity than Si single crystals. . Therefore, it is possible to realize high power, high frequency, withstand voltage, environmental resistance, etc. that cannot be realized with existing semiconductor materials such as Si single crystal and GaAs single crystal, and power devices that enable high power control and energy saving. Expectations are growing as next-generation semiconductor materials in a wide range of materials, high-speed and large-capacity information communication device materials, in-vehicle high-temperature device materials, radiation-resistant device materials, and the like.

  Conventionally, as a method for growing a SiC single crystal, a gas phase method, an Acheson method, and a solution method are typically known. Among the vapor phase methods, for example, the sublimation method has a defect that a grown single crystal is liable to cause a lattice defect such as a hollow through defect called a micropipe defect or a stacking fault and a crystal polymorphism, but the crystal growth. Due to the high speed, many of SiC bulk single crystals are conventionally produced by a sublimation method. Attempts have also been made to reduce defects in the grown crystal, and the dislocation density propagates in the <0001> direction by repeatedly growing crystals on the (11-20) plane and the (1-100) plane by the sublimation method. Has been proposed (Patent Document 1). In the Atchison method, since silica and coke are used as raw materials and heated in an electric furnace, it is impossible to obtain a single crystal with high crystallinity due to impurities in the raw materials.

  In the solution method, an Si melt or an alloy is melted into the Si melt in a graphite crucible, C is dissolved in the melt, and a SiC crystal layer is deposited on a seed crystal substrate placed in a low temperature portion to grow. Is the method. Since the crystal growth is performed in the solution method in a state close to thermal equilibrium as compared with the gas phase method, it can be expected to reduce defects. For this reason, recently, several methods for producing an SiC single crystal by a solution method have been proposed (Patent Document 2), and a method for obtaining an SiC single crystal with few crystal defects has been proposed (Patent Document 3).

JP 2003-119097 A JP 2008-105896 JP-A-6-227886

  As described in Patent Documents 1 to 3, attempts have been made to reduce defects in grown crystals in the sublimation method or the solution method. However, in order to stably obtain a high-quality SiC single crystal that can be used as a semiconductor element, the above method is still insufficient, and in particular, an SiC single crystal that does not contain threading dislocations is manufactured with a high yield. That is still difficult. In the sublimation method, it is difficult to obtain a single crystal containing almost or no threading dislocations. Even in the solution method, the dislocations of the seed crystals are easily propagated, and the crystals grown in the direction perpendicular to the growth surface of the seed crystals are obtained. It is difficult to obtain a single crystal containing substantially no or no threading dislocations.

  The present invention solves the above-mentioned problems, and provides a high-quality SiC single crystal with reduced threading dislocation density such as threading screw dislocations, threading edge dislocations, and micropipe defects, and a method for producing such a SiC single crystal. The purpose is to provide.

The present invention is a method for producing a SiC single crystal by a solution method in which a SiC single crystal is grown by bringing a SiC seed crystal into contact with a Si-C solution having a temperature gradient that decreases in temperature from the inside toward the surface,
The temperature gradient of the surface region of the Si—C solution is 10 ° C./cm or less,
The SiC single crystal is brought into contact with the (1-100) plane of the SiC seed crystal in the Si-C solution, and the SiC single crystal is less than 20 × 10 ⁻⁴ cm ² / h · ° C. Growing at a ratio of SiC single crystal growth rate to temperature gradient (single crystal growth rate / temperature gradient);
Is a method for producing a SiC single crystal.

  The present invention is also a SiC single crystal grown from an SiC seed crystal, wherein the threading dislocation density in the (0001) plane is smaller than the threading dislocation density in the (0001) plane of the seed crystal. is there.

  According to the present invention, a SiC single crystal having a low threading dislocation density in the (0001) plane can be obtained.

It is a cross-sectional schematic diagram of the single crystal manufacturing apparatus by the solution method which can be used in this invention. It is an external appearance photograph of the growth surface of the SiC single crystal grown on the (1-100) plane concerning the present invention. It is the microscope picture of the (0001) plane which cut out the (0001) plane from the (1-100) plane growth crystal based on the seed crystal concerning the present invention, and carried out the fusion alkali etching. It is the photograph which expanded and observed about the seed crystal part of FIG. FIG. 4 is a photograph of an enlarged observation of a grown crystal part in FIG. 3. It is an external appearance photograph of the growth surface of the crystal grown by (11-20) plane. It is an external appearance photograph of the growth surface of the crystal grown by (1-100) plane. It is the graph showing the growth condition range by the temperature gradient of the surface area | region of a Si-C solution in (1-100) plane growth, and the ratio of single crystal growth rate / temperature gradient.

  In the present specification, “−1” in the notation of the (1-100) plane and the like is a place where “−1” is originally written with a horizontal line on the number.

  As described in Patent Document 1, the RAF growth method has hitherto been considered effective for reducing the dislocation of crystals, and (11-20) plane (also referred to as a plane) growth and (1- A crystal with reduced dislocations is produced by repeating 100) plane (also referred to as m-plane) growth. However, it is difficult to obtain a dislocation-free single crystal even by the RAF method, and it is necessary to repeatedly grow the (11-20) plane and the (1-100) plane, and the dislocation density can be further reduced and simplified. New manufacturing methods are desired.

  In the production of SiC single crystals by the solution method, the present inventor has found that the threading dislocation density such as screw dislocations, edge dislocations, and micropipe defects that can occur in the grown crystal due to the seed crystal can be reduced as compared with the prior art. We conducted intensive research on quality SiC single crystals.

  As a result, by performing m-plane growth based on the (1-100) plane (also referred to as m-plane) of the seed crystal using the solution method, instead of the a-plane growth that has been typically performed conventionally, It has been found that a SiC single crystal having a threading dislocation density lower than that of a seed crystal can be obtained. Further, according to this method, it has been found that it is not necessary to repeatedly grow a single crystal, and an SiC single crystal having a significantly reduced threading dislocation density than that of a seed crystal can be obtained by one m-plane growth.

  Furthermore, it has been found that the temperature gradient of the surface region of the Si—C solution and the growth rate of the single crystal with respect to the temperature gradient influence the flatness of the growth surface of the SiC single crystal. And the manufacturing method of the SiC single crystal which incorporated the temperature gradient of the surface area | region of this Si-C solution and the conditions of the growth rate of a single crystal was discovered.

The present invention is a method for producing a SiC single crystal by a solution method in which a SiC single crystal is grown by bringing a SiC seed crystal into contact with a Si-C solution having a temperature gradient that decreases in temperature from the inside toward the surface,
The temperature gradient of the surface region of the Si—C solution is 10 ° C./cm or less,
The SiC single crystal is brought into contact with the (1-100) plane of the SiC seed crystal in the Si-C solution, and the SiC single crystal is less than 20 × 10 ⁻⁴ cm ² / h · ° C. And a method of manufacturing a SiC single crystal, comprising growing at a ratio of a growth rate of the SiC single crystal to a temperature gradient (growth rate of single crystal / temperature gradient).

In this method, the SiC single crystal is grown from a seed crystal as a starting point, has a flat growth surface, and the threading dislocation density in the (0001) plane is the threading dislocation density in the (0001) plane of the seed crystal. A SiC single crystal having a smaller threading dislocation density of 1 / cm ² or less, more preferably zero threading dislocation density can be obtained.

  In the method for producing a SiC single crystal of the present invention, a solution method is used. The solution method for producing a SiC single crystal is to supersaturate the surface region of the Si-C solution by forming a temperature gradient in the crucible that decreases in temperature from the inside of the Si-C solution toward the surface of the solution. In this method, an SiC single crystal is grown on the seed crystal using the seed crystal brought into contact with the Si-C solution as a base point.

  In this method, a SiC single crystal of a quality generally used for the production of an SiC single crystal can be used as a seed crystal. For example, a SiC single crystal generally prepared by a sublimation method can be used as a seed crystal. The SiC single crystal generally produced by such a sublimation method generally contains many threading dislocations and basal plane dislocations.

In this method, an SiC seed crystal having a (1-100) plane is used, and a SiC single crystal is grown on a (1-100) plane by using the solution method with the (1-100) plane as a base point. The threading dislocation density in the (0001) plane of the obtained (1-100) plane grown SiC single crystal is smaller than the threading dislocation density in the (0001) plane of the seed crystal, and preferably the threading dislocation density is 1 / cm ^2. Or more preferably, the threading dislocation density is zero. The seed crystal can have any shape such as a plate shape, a disc shape, a columnar shape, a prism shape, a truncated cone shape, or a truncated pyramid shape. The (1-100) plane of the seed crystal can be used as the lower surface of the seed crystal that makes contact with the Si-C solution surface, and the upper surface on the opposite side can be used as a surface that is held by a seed crystal holding shaft such as a graphite shaft. .

The temperature gradient of the surface region of the Si—C solution is a temperature gradient in the vertical direction of the surface of the Si—C solution, and is a temperature gradient that decreases in temperature from the inside of the Si—C solution toward the surface of the solution. For the temperature gradient, a temperature A on the surface of the Si—C solution on the low temperature side and a temperature B on the high temperature side at a predetermined depth perpendicular to the solution side from the surface of the Si—C solution are measured with a thermocouple, The temperature difference can be calculated by dividing the temperature A and the temperature B by the distance between the measured positions. For example, when measuring the temperature gradient between the surface of the Si—C solution and the position of the depth Dcm perpendicular to the solution side from the surface of the Si—C solution, the surface temperature A of the Si—C solution and Si -C Difference from temperature B at a position of depth Dcm perpendicular to the solution side from the surface of the solution divided by Dcm:
Temperature gradient (° C./cm)=(B−A)/D
Can be calculated.

  In this method, the temperature gradient of the surface region of the Si—C solution is 10 ° C./cm or less. It has been found that by making the temperature gradient of the surface region of the SiC solution within the above range, it becomes easy to obtain a SiC single crystal having no flat threading dislocation and having a flat surface.

  If the temperature gradient in the vicinity of the seed crystal substrate is large, the growth rate of the SiC single crystal can be increased. However, if the temperature gradient is too large, it becomes difficult to obtain a flat growth surface, so it is necessary to control the temperature gradient within the above range. There is.

  The lower limit of the temperature gradient of the surface region of the Si—C solution is not particularly limited, and may be, for example, 2 ° C./cm or more, 4 ° C./cm or more, 6 ° C./cm or more, or 8 ° C./cm or more.

  The control range of the temperature gradient is preferably a range from the surface of the Si—C solution to a depth of 3 mm, more preferably a depth of 20 mm.

  If the control range of the temperature gradient is too shallow, the range for controlling the temperature gradient is shallow and the range for controlling the degree of supersaturation of C becomes shallow, and the growth of the SiC single crystal may become unstable. Further, if the range for controlling the temperature gradient is deep, the range for controlling the degree of supersaturation of C is also deep and effective for stable growth of the SiC single crystal. In practice, however, the depth contributing to the growth of the single crystal is Si −. The range is from the surface of the C solution to a depth of several mm. Therefore, in order to stably perform the growth of the SiC single crystal and the control of the temperature gradient, it is preferable to control the temperature gradient in the depth range.

  The control of the temperature gradient of the surface region of the Si-C solution will be described in detail later with reference to the drawings. The arrangement, configuration, and output of a heating device such as a high-frequency coil arranged around the crucible of the single crystal manufacturing apparatus. By adjusting etc., a predetermined temperature gradient in the vertical direction can be formed on the surface of the Si—C solution.

In this method, the ratio of the growth rate (μm / h) of the SiC single crystal to the temperature gradient (° C./cm) of the surface region of the Si—C solution (growth rate / temperature gradient of the single crystal) is 20 × 10 ^{− The} SiC single crystal is grown under a control of less than ⁴ cm ² / h · ° C., preferably less than 12 × 10 ⁻⁴ cm ² / h · ° C. In addition to controlling the temperature gradient of the surface region of the Si-C solution, by adjusting the growth rate of the single crystal with respect to the temperature gradient within the above range, the SiC single crystal that does not contain threading dislocations and has a flat surface is stabilized. I found out that

  The growth rate of the SiC single crystal can be controlled by controlling the degree of supersaturation of the Si—C solution. Increasing the supersaturation degree of the Si—C solution increases the growth rate of the SiC single crystal, and decreasing the supersaturation degree decreases the growth rate of the SiC single crystal.

  The supersaturation degree of the Si-C solution can be controlled mainly by the surface temperature of the Si-C solution and the temperature gradient of the surface region of the Si-C solution. For example, the surface temperature of the Si-C solution is kept constant. However, if the temperature gradient of the surface region of the Si—C solution is reduced, the degree of supersaturation can be reduced, and if the temperature gradient of the surface region of the Si—C solution is increased, the degree of supersaturation can be increased.

  Note that even if the heat removal through the seed crystal holding axis is changed, the supersaturation degree of the Si—C solution in the vicinity of the seed crystal may change and the growth rate of the SiC single crystal may change. Therefore, changing the thermal conductivity by selecting the material of the seed crystal holding shaft, or changing the growth rate of the SiC single crystal by changing the degree of heat removal by changing the diameter of the seed crystal holding shaft, etc. You can also.

  The evaluation of the presence or absence of threading dislocations is performed by mirror polishing so that the (0001) plane is exposed, performing molten alkali etching using molten potassium hydroxide, sodium peroxide, etc. This can be done by microscopic observation of the surface.

  As described above, the seed crystal can be installed in the single crystal manufacturing apparatus by holding the upper surface of the seed crystal on the seed crystal holding shaft.

  The contact of the seed crystal with the Si-C solution is performed by lowering the seed crystal holding axis holding the seed crystal toward the Si-C solution surface, and with the lower surface of the seed crystal parallel to the Si-C solution surface. It can be performed by contacting with a -C solution. Then, the SiC single crystal can be grown by holding the seed crystal at a predetermined position with respect to the Si—C solution surface.

  The holding position of the seed crystal is such that the position of the lower surface of the seed crystal coincides with the Si-C solution surface, is below the Si-C solution surface, or is above the Si-C solution surface. There may be. When the lower surface of the seed crystal is held at a position above the Si-C solution surface, the seed crystal is once brought into contact with the Si-C solution and the Si-C solution is brought into contact with the lower surface of the seed crystal. Pull up into place. The position of the lower surface of the seed crystal may coincide with the Si-C solution surface or be lower than the Si-C solution surface, but in order to prevent the occurrence of polycrystals, Si It is preferable to prevent the -C solution from contacting. In these methods, the position of the seed crystal may be adjusted during the growth of the single crystal.

  The seed crystal holding axis may be a graphite axis that holds the seed crystal substrate on its end face. The seed crystal holding shaft may have an arbitrary shape such as a columnar shape or a prismatic shape, and a graphite shaft having the same end surface shape as the shape of the upper surface of the seed crystal may be used.

  An SiC single crystal can be further grown using the SiC single crystal grown by the present method as a seed crystal. The SiC single crystal grown by (1-100) plane by this method contains a few basal plane dislocations but very few or zero threading dislocations. Therefore, the (000-1) plane of this SiC single crystal is When the crystal is further grown as a base point, it is possible to obtain a very high quality SiC single crystal that includes not only threading dislocations but also basal plane dislocations. This is because there is very little or no threading dislocations in the (000-1) plane which is the growth base point of the seed crystal, so there is very little or no threading dislocation propagating from the seed crystal to the growth crystal; This is because basal plane dislocations that can be included in the seed crystal are difficult to propagate to the (000-1) plane grown crystal. This can be done using the solution method or can be done using the sublimation method.

  In the present invention, the Si—C solution refers to a solution in which C is dissolved using a melt of Si or Si / X (X is one or more metals other than Si) as a solvent. X is one or more kinds of metals, and is not particularly limited as long as it can form a liquid phase (solution) in thermodynamic equilibrium with SiC (solid phase). Examples of suitable metals X include Ti, Mn, Cr, Ni, Ce, Co, V, Fe and the like.

  The Si—C solution is preferably a Si—C solution using a melt of Si / Cr / X (X is one or more metals other than Si and Cr) as a solvent. Furthermore, a Si—C solution using a melt of Si / Cr / X = 30 to 80/20 to 60/0 to 10 in terms of atomic composition percentage as a solvent is preferable since there is little variation in the dissolved amount of C. For example, in addition to Si, Cr, Ni, or the like can be charged into the crucible to form a Si—Cr solution, a Si—Cr—Ni solution, or the like.

  The surface temperature of the Si—C solution is preferably 1800 to 2200 ° C. with little variation in the amount of C dissolved in the Si—C solution.

  The temperature of the Si—C solution can be measured using a thermocouple, a radiation thermometer, or the like. Regarding the thermocouple, from the viewpoint of high temperature measurement and prevention of impurity contamination, a thermocouple in which a tungsten-rhenium strand coated with zirconia or magnesia glass is placed in a graphite protective tube is preferable.

  FIG. 1 shows an example of a SiC single crystal manufacturing apparatus suitable for carrying out the method of the present invention. The illustrated SiC single crystal manufacturing apparatus 100 includes a crucible 10 containing a Si-C solution 24 in which C is dissolved in a Si or Si / X melt, and is provided on the surface of the solution from the inside of the Si-C solution. A SiC single crystal can be grown by forming a temperature gradient that decreases toward the surface and bringing the seed crystal substrate 14 held at the tip of the graphite shaft 12 that can be moved up and down into contact with the Si-C solution 24. It is preferable to rotate the crucible 10 and the graphite shaft 12.

  The Si-C solution 24 is prepared by charging a raw material into a crucible and dissolving C in a Si or Si / X melt prepared by heating and melting. By making the crucible 10 a carbonaceous crucible such as a graphite crucible or an SiC crucible, C is dissolved in the melt by melting the crucible 10 to form an Si-C solution. In this way, undissolved C does not exist in the Si—C solution 24, and waste of SiC due to precipitation of the SiC single crystal in the undissolved C can be prevented. The supply of C may be performed by, for example, a method of injecting hydrocarbon gas or charging a solid C supply source together with the melt raw material, or combining these methods with melting of a crucible. Also good.

  In order to keep warm, the outer periphery of the crucible 10 is covered with a heat insulating material 18. These are collectively accommodated in the quartz tube 26. A high frequency coil 22 for heating is disposed on the outer periphery of the quartz tube 26. The high frequency coil 22 may be composed of an upper coil 22A and a lower coil 22B, and the upper coil 22A and the lower coil 22B can be independently controlled.

  Since the crucible 10, the heat insulating material 18, the quartz tube 26, and the high frequency coil 22 become high temperature, they are disposed inside the water cooling chamber. The water-cooled chamber includes a gas inlet and a gas outlet in order to make it possible to adjust the atmosphere in the apparatus to Ar, He, or the like.

  The temperature of the Si—C solution usually has a temperature distribution in which the surface temperature is lower than the inside of the Si—C solution due to radiation or the like. Further, the number and interval of the high frequency coil 22, the high frequency coil 22 and the crucible 10 By adjusting the positional relationship in the height direction and the output of the high-frequency coil, the Si—C solution 24 is so heated that the upper part of the solution in which the seed crystal substrate 14 is immersed is at a low temperature and the lower part of the solution is at a high temperature. A predetermined temperature gradient in the vertical direction can be formed on the surface of the solution 24. For example, the output of the upper coil 22A can be made smaller than the output of the lower coil 22B, and a predetermined temperature gradient can be formed in the Si—C solution 24 such that the upper part of the solution is low and the lower part of the solution is high.

  C dissolved in the Si-C solution 24 is dispersed by diffusion and convection. The vicinity of the lower surface of the seed crystal substrate 14 has a lower temperature than the lower part of the Si-C solution 24 due to the output control of the upper / lower stages of the coil 22, heat radiation from the surface of the Si—C solution, and heat removal through the graphite shaft 12. A temperature gradient is formed. When C dissolved in the lower part of the solution having a high solubility at a high temperature reaches near the lower surface of the seed crystal substrate having a low solubility at a low temperature, a supersaturated state is obtained, and an SiC single crystal grows on the seed crystal substrate using this supersaturation as a driving force.

  In some embodiments, before the growth of the SiC single crystal, meltback may be performed to dissolve and remove the surface layer of the SiC seed crystal substrate in the Si—C solution. The surface layer of the seed crystal substrate on which the SiC single crystal is grown may have a work-affected layer such as dislocations or a natural oxide film, which must be dissolved and removed before the SiC single crystal is grown. However, it is effective for growing a high-quality SiC single crystal. Although the thickness to melt | dissolves changes with the processing state of the surface of a SiC seed crystal substrate, about 5-50 micrometers is preferable in order to fully remove a process deterioration layer and a natural oxide film.

  The meltback can be performed by forming a temperature gradient in the Si-C solution in which the temperature increases from the inside of the Si-C solution toward the surface of the solution, that is, a temperature gradient opposite to the SiC single crystal growth. it can. The temperature gradient in the reverse direction can be formed by controlling the output of the high frequency coil.

  Melt back can also be performed by immersing the seed crystal substrate in a Si—C solution heated to a temperature higher than the liquidus temperature without forming a temperature gradient in the Si—C solution. In this case, the higher the Si-C solution temperature, the higher the dissolution rate, but it becomes difficult to control the amount of dissolution, and the lower the temperature, the slower the dissolution rate.

  In some embodiments, the seed crystal substrate may be preheated before contacting the seed crystal substrate with the Si-C solution. When a low-temperature seed crystal substrate is brought into contact with a high-temperature Si—C solution, heat shock dislocation may occur in the seed crystal. Heating the seed crystal substrate before bringing the seed crystal substrate into contact with the Si—C solution is effective for preventing thermal shock dislocation and growing a high-quality SiC single crystal. The seed crystal substrate can be heated by heating the entire graphite axis. Alternatively, instead of this method, the Si—C solution may be heated to a temperature at which the crystal grows after contacting the seed crystal with a relatively low temperature Si—C solution. This case is also effective for preventing heat shock dislocation and growing a high-quality SiC single crystal.

The present invention is also directed to a SiC single crystal grown from a seed crystal as a starting point, wherein the threading dislocation density in the (0001) plane is smaller than the threading dislocation density in the (0001) plane of the seed crystal. And The threading dislocation density in the (0001) plane of the SiC single crystal is preferably 1 piece / cm ² or less, more preferably zero.

(Example 1)
An SiC single crystal having a thickness of 0.8 mm and a 10 mm square plate-like 4H—SiC single crystal having a lower surface having a (1-100) plane was prepared and used as a seed crystal substrate. The upper surface of the seed crystal substrate is placed at the substantially central portion of the end surface of the cylindrical graphite shaft having a length of 20 cm and a diameter of 12 mm, and the end surface of the graphite shaft does not protrude from the upper surface of the seed crystal and enters the upper surface of the seed crystal. Bonding was performed using a graphite adhesive.

  Using a single crystal manufacturing apparatus shown in FIG. 1, a raw material for a melt in a ratio of 50:40:10 of Si / Cr / Ni in an atomic composition percentage in a graphite crucible having an inner diameter of 40 mm and a height of 185 mm containing an Si—C solution. It was charged as. The air inside the single crystal production apparatus was replaced with argon. The raw material in the graphite crucible was melted by energizing and heating the high frequency coil to form a Si / Cr / Ni alloy melt. Then, a sufficient amount of C was dissolved from the graphite crucible into the Si / Cr / Ni alloy melt to form a Si-C solution.

  The graphite crucible was heated by adjusting the outputs of the upper and lower coils, and the temperature on the surface of the Si—C solution was raised to 1820 ° C. The temperature was measured using a thermocouple in which a tungsten-rhenium strand capable of raising and lowering was placed in a graphite protective tube. While maintaining the lower surface of the seed crystal bonded to the graphite shaft so as to be parallel to the Si-C solution surface, the position of the lower surface of the seed crystal is arranged at a position corresponding to the liquid surface of the Si-C solution, A seed touch was made to contact the lower surface of the seed crystal.

  Further, the temperature at the surface of the Si—C solution is raised to 1930 ° C., and the temperature gradient that decreases from the inside of the solution toward the solution surface within the range of 20 mm from the solution surface is controlled to 8.6 ° C./cm. The crystal was grown.

  After the completion of crystal growth, the graphite axis was raised, and the seed crystal and the SiC crystal grown from the seed crystal as a base point were separated from the Si-C solution and the graphite axis and collected. The obtained grown crystal was a single crystal, and the growth rate was 45 μm / h. FIG. 2 shows a photograph of the grown single crystal observed from the growth surface. The growth surface of the obtained single crystal was flat as shown in FIG.

(Example 2)
The crystal was grown and recovered under the same conditions as in Example 1 except that the temperature at the surface of the Si-C solution when growing the crystal was 2030 ° C. and the temperature gradient was 9.0 ° C./cm. .

  The obtained grown crystal was a single crystal, and the growth rate was 100 μm / h. The growth surface of the obtained single crystal was flat like the single crystal grown in Example 1.

(Example 3)
The crystal was grown and collected under the same conditions as in Example 1 except that the temperature at the surface of the Si-C solution when growing the crystal was 1920 ° C. and the temperature gradient was 9.3 ° C./cm. .

  The obtained grown crystal was a single crystal, and the growth rate was 80 μm / h. The growth surface of the obtained single crystal was flat like the single crystal grown in Example 1.

Example 4
The crystal was grown and collected under the same conditions as in Example 1 except that the temperature on the surface of the Si-C solution when growing the crystal was 1920 ° C. and the temperature gradient was 9.0 ° C./cm. .

  The obtained grown crystal was a single crystal, and the growth rate was 60 μm / h. The growth surface of the obtained single crystal was flat like the single crystal grown in Example 1.

(Example 5)
A plate-shaped 4H—SiC single crystal having a thickness of 3.5 mm and a 10 mm square, prepared by a sublimation method with a lower surface having a (1-100) plane, is used as a seed crystal substrate, and the crystal is grown. Example except that the temperature on the surface of the Si—C solution at 2000 ° C. was 2000 ° C., the seed crystal was seed-touched to the 2000 ° C. Si—C solution, and the temperature gradient was 10.0 ° C./cm Crystals were grown and recovered under the same conditions as in 1.

  The obtained grown crystal was a single crystal, and the growth rate was 60 μm / h. The growth surface of the obtained single crystal was flat like the single crystal grown in Example 1.

(Example 6)
Except that a plate-like 4H—SiC single crystal having a thickness of 2.0 mm and a 10 mm square, prepared by a sublimation method having a lower surface having a (1-100) plane, was used as a seed crystal substrate. Under the same conditions as in Example 5, crystals were grown and recovered.

  The obtained growth crystal was a single crystal, and the growth rate was 101 μm / h. The growth surface of the obtained single crystal was flat like the single crystal grown in Example 1.

(Example 7)
Except that a plate-shaped 4H—SiC single crystal having a thickness of 1.5 mm and a 10 mm square, prepared by a sublimation method having a lower surface having a (1-100) plane, was used as a seed crystal substrate. Under the same conditions as in Example 5, crystals were grown and recovered.

  The obtained growth crystal was a single crystal, and the growth rate was 132 μm / h. The growth surface of the obtained single crystal was flat like the single crystal grown in Example 1.

(Observation of threading dislocation)
Each of the SiC single crystals grown in Examples 1 to 7 was cut with a diamond saw so as to expose the (0001) plane, and polished with two types of diamond slurries (slurry particle size: 6 μm and 3 μm) to obtain a mirror surface. Finished. Next, each grown SiC single crystal is immersed for 5 minutes in a melt of 500 ° C. in which potassium hydroxide (manufactured by Nacalai Tesque Co., Ltd.) and potassium peroxide (manufactured by Wako Pure Chemical Industries, Ltd.) are mixed. went. Each SiC single crystal was taken out from the mixed melt, subjected to ultrasonic cleaning in pure water, and then observed for dislocation by microscopic observation (manufactured by Nikon).

  3 to 5 show micrographs of the (0001) plane obtained by subjecting the single crystal obtained in Example 1 to molten alkali etching. FIG. 3 is an overall photograph including the seed crystal 14 and the growth crystal 30, and FIG. 4 shows an enlarged photograph of the portion 32 observed by magnifying the seed crystal 14 in FIG. A photograph is shown in FIG. From the observation of the seed crystal, threading screw dislocation (TSD) and threading edge dislocation (TED) were detected, but the basal plane dislocation (BPD) was slightly observed in the grown crystal, but threading screw dislocation (TSD). It was found that threading dislocations such as threading edge dislocations (TED) and micropipe defects were not detected and threading dislocations were not included. Similarly, threading dislocations were not detected from the single crystals grown in Examples 2 to 7, and it was found that threading dislocations were not included.

(Comparative Example 1)
A plate-like 4H—SiC single crystal having a thickness of 1 mm and 10 mm and having a (11-20) plane was prepared and used as a seed crystal substrate with the (11-20) plane as the bottom surface. In the same manner as in Example 1, the upper surface of the seed crystal substrate was bonded to a substantially central portion of the end surface of the graphite shaft using a graphite adhesive.

  Then, the crystal was grown under the same conditions as in Example 1 except that the temperature at the surface of the Si—C solution when growing the crystal was 1930 ° C. and the temperature gradient was 8.2 ° C./cm, It was collected.

  FIG. 6 shows a photograph of the grown crystal observed from the growth surface. As shown in FIG. 6, the growth surface of the obtained crystal was severely rough, a flat surface was not formed, and it was found that no single crystal was grown.

(Comparative Example 2)
The crystal was grown and collected under the same conditions as in Example 1 except that the temperature on the surface of the Si-C solution when growing the crystal was 1890 ° C. and the temperature gradient was 10.3 ° C./cm. .

  The growth rate of the obtained crystal was 83 μm / h. FIG. 7 shows a photograph of the grown crystal observed from the growth surface. The obtained crystal was a single crystal, but the growth surface was rough as shown in FIG. 7, and a flat surface was not obtained.

(Comparative Example 3)
The crystal was grown and recovered under the same conditions as in Example 1 except that the temperature at the surface of the Si-C solution when growing the crystal was 1870 ° C. and the temperature gradient was 12.0 ° C./cm. .

  The growth rate of the obtained crystal was 144 μm / h. Although the obtained crystal was a single crystal, the growth surface was rough as in Comparative Example 2, and a flat surface was not obtained.

(Comparative Example 4)
The crystal was grown and collected under the same conditions as in Example 1 except that the temperature at the surface of the Si-C solution when growing the crystal was 2000 ° C. and the temperature gradient was 15.0 ° C./cm. .

  The growth rate of the obtained crystal was 144 μm / h. Although the obtained crystal was a single crystal, the growth surface was rough as in Comparative Example 2, and a flat surface was not obtained.

(Comparative Example 5)
The crystal was grown and recovered under the same conditions as in Example 1 except that the temperature at the surface of the Si-C solution when growing the crystal was 1990 ° C. and the temperature gradient was 8.6 ° C./cm. .

  The crystal growth rate obtained was 172 μm / h. Although the obtained crystal was a single crystal, the growth surface was rough as in Comparative Example 2, and a flat surface was not obtained.

  In Table 1, in Examples 1-7 and Comparative Examples 1-5, the growth surface, the temperature of the Si-C solution surface, the temperature gradient of the surface region of the Si-C solution, the type of crystals obtained, the crystal growth rate, And the growth rate / temperature gradient ratio. FIG. 8 shows the temperature gradient of the surface region of the Si—C solution and the ratio of the single crystal growth rate / temperature gradient in the (1-100) plane growth of Examples 1 to 7 and Comparative Examples 2 to 5. The optimum growth condition range is shown.

A single crystal could not be obtained by (11-20) plane growth, but a single crystal could be obtained by growing in the (1-100) plane. Furthermore, the temperature gradient of the surface region of the Si—C solution is 10 ° C./cm or less, and the ratio of the crystal growth rate to the temperature gradient (growth rate / temperature gradient) is 20 (10 ⁻⁴ cm ² / (h · ° C.). The SiC single crystal which has a flat surface and does not contain threading dislocations on the (0001) plane was obtained by crystal growth under the condition of less than.

DESCRIPTION OF SYMBOLS 100 Single crystal manufacturing apparatus 10 Graphite crucible 12 Graphite shaft 14 Seed crystal substrate 18 Thermal insulation material 22 High frequency coil 22A Upper high frequency coil 22B Lower high frequency coil 24 Si-C solution 26 Quartz tube 30 SiC growth single crystal 32 Enlarged observation part of seed crystal part 34 Magnified observation of the growing single crystal part

Claims (4)

A method for producing a SiC single crystal by a solution method, wherein a SiC single crystal is grown by bringing a SiC seed crystal into contact with a Si-C solution having a temperature gradient that decreases from the inside toward the surface,
The temperature gradient of the surface region of the Si-C solution is 10 ° C./cm or less,
(1-100) plane of the SiC seed crystal is brought into contact with the Si-C solution, and an SiC single crystal is placed on the (1-100) plane of the seed crystal at 20 × 10 ⁻⁴ cm ² / h · Growing at a ratio of the growth rate of the SiC single crystal to the temperature gradient (single crystal growth rate / temperature gradient) of less than ° C.
The manufacturing method of the SiC single crystal containing this.   A method for producing a SiC single crystal, comprising the step of crystal growth using the SiC single crystal produced by the method according to claim 1 as a seed crystal and using the (000-1) plane of the seed crystal as a base point.   A SiC single crystal grown from a SiC seed crystal as a starting point, wherein the threading dislocation density in the (0001) plane is smaller than the threading dislocation density in the (0001) plane of the seed crystal.   The SiC single crystal according to claim 3, wherein the threading dislocation density in the (0001) plane is zero.